1. Field of the Invention:
This invention relates to a silver halide photographic light-sensitive material and a process for forming a high contrast photographic image. More particularly, it is a process for forming a high contrast negative image which is suitable for use in a photomechanical process for making a photographic printing plate.
2. Description of the Prior Art:
A photomechanical process is required to form a sharp dot or line image and therefore must use a system which can form a high contrast image particularly having a gamma value of at least 10. Accordingly, it has been usual to employ a lith type silver halide photographic light-sensitive material comprising a silver chlorobromide emulsion containing over 50 mol %, or preferably over 70 mol %, of silver chloride and treat it with a so called lith developer containing only hydroquinone as a developing agent and having a very low free sulfite ion concentration usually not exceeding 0.1 mol per liter. This developer is, however, very unstable due to its low sulfite ion concentration. A lith developer is easily oxidized with air and causes a drastic deterioration in quality within only a few days. Moreover, the use of the emulsion having such a high silver chloride content makes it difficult to achieve high sensitivity.
U.S. Pat. Nos. 4,168,977, 4,224,401, 4,241,164, 4,269,929, 4,311,781, and 4,650,746 disclose processes which employ specific hydrazine derivatives and stable developers to form a high contrast image. These processes employ silver halide photographic light-sensitive materials of the surface latent image type containing specific hydrazine derivatives (usually acylphenylhydrazine derivatives) as nucleating agents and treat them with stable developers containing at least 0.5 mol of sulfite ion per liter and having a pH of 11 to 12.3 to form a high contrast impage having a gamma value of over 10. The presence of a high concentration of sulfite ion in these developers greatly improves their storage stability over that of the lith developers.
These processes can form a high contrast negative image, but have also been found to present a number of problems including the appearance of "pepper" which causes a serious problem in a photomechanical process for making printing plates. The pepper is a black spot which appears in an unexposed area, such as an area between dots which is not to be developed. The appearance of pepper seriously lowers the commercial value of graphic arts materials. A great deal of efforts have, therefore, been made to explore techniques for preventing the appearance of pepper, but the improvement in pepper susceptibility has often resulted in a reduction in sensitivity and gamma value. Accordingly, it has been a strong desire to develop a system which can form a high contrast impage having high sensitivity without the appearance of any pepper.